The process of homogeneously blending solid or wax-like non-readily soluble flame retardants in the liquid precursors of polyurethane foams typically needs to be carried out with heating. It would be beneficial to provide the flame retardant in the form of a preformed liquid composition, thereby obviating the need to perform the blending process with the polyurethane foam precursors under heating, and thus considerably simplifying the process of manufacturing the foam. This may be especially useful in view of the fact that the preparation of polyurethane foams is very often carried out outdoors, e.g., at construction sites.
Attempts to address the aforementioned problem are described in WO 03/060000 and U.S. Pat. No. 4,717,509, which refer to the use of tetrabromobisphenol A and tribromoneopentyl alcohol, respectively, as flame retardants for rigid polyurethane foams.
The present invention is concerned with the class of flame retardants obtainable by reacting tetrabromobisphenol A (chemically named 4,4′-isopropylidene-bis(2,6-dibromophenol) with epichlorohydrin (chemically named chloromethyl oxirane). The reaction of tetrabromobisphenol A with epichlorohydrin is known to yield various reactive epoxides having high bromine content, which may be used as such, or in the form of their end-capped derivatives, as flame retardants in polymeric compositions. The aforementioned epoxides and end-capped derivatives thereof are identified by formula (1):
wherein n, the degree of polymerization, is an integer in the range between 0 and 5, and more preferably in the range between 0 and 4, and R1 and R2 are independently selected from the group consisting of the following monovalent radicals:

The compounds of formula (1) were proposed in JP 64-074262 and JP 64-074263 for use in connection with thermoplastic polyurethanes.